The present invention relates to a piezoelectric resonator unit and a temperature control method therefor, and to a piezoelectric oscillator.
Excellent frequency accuracy with respect to changes in the temperature of the surroundings are demanded in piezoelectric resonator units. In order to control the frequency of a piezoelectric resonator, the temperature of the piezoelectric resonator is detected and the piezoelectric resonator is heated in order to minimize changes that occurs in the frequency characteristics of the piezoelectric resonator as a result of temperature fluctuations. For example, Japanese Unexamined Patent Application Publication No. 2013-62707 discloses a piezoelectric device that is configured to detect the temperature of a piezoelectric resonator using a temperature-sensing component that is bonded to an outer surface of the piezoelectric resonator.
According to the configuration disclosed in the foregoing published application, the terminals of the temperature-sensing component are arranged on the outer surface of a package in which the piezoelectric resonator is housed. As a result, an error in the detected temperature may be large and it may take time until the temperature is detected. Consequently, it may not be possible to accurately control the frequency characteristic of the piezoelectric resonator.
BRIEF DESCRIPTION OF THE INVENTION
The present invention was made in light of the above-described circumstances, and it is one object of the invention to provide a piezoelectric resonator unit and a temperature control method therefor, and a piezoelectric oscillator in which the temperature of a piezoelectric resonator can be accurately detected and temperature control can be appropriately performed on the piezoelectric resonator.
In accordance with one aspect of the invention, a piezoelectric resonator unit, comprises a base having a mounting surface, a piezoelectric resonator mounted on the mounting surface, and a lid which is bonded to the mounting surface such that the piezoelectric resonator is hermetically sealed in an inner space. A heat conductor extends from a position outside of the inner space to a position in the inner space to provide a thermal connection to a temperature sensor and a heating element so that when the temperature sensor and the heating element are connected to the heat conductor from a position outside of the inner space, the heat conductor can apply heat to the inner space and the temperature sensor can sense the temperature of the inner space.
In one embodiment, a portion of the heat conductor is located on the mounting surface of the base member.
In some embodiments the piezoelectric resonator is mounted on the base member via an electrically conductive holding member and a portion of the heat conductor overlaps at least part of the piezoelectric resonator but does not touch the electrically conductive holding member.
In various embodiments, the piezoelectric resonator is a crystal resonator. In some embodiments, both the base member and the lid member are composed of a crystal material.
In some preferred embodiments the crystal resonator includes crystal blank having a main surface, an excitation electrode formed on the main surface, and a frame body that surrounds an outer periphery of the crystal blank and is connected to the crystal blank by a connection portion.
In some embodiments, the heat conductor includes a portion located on the frame body in the inner space. In other embodiments, the heat conductor includes a portion located on the connection portion in the inner space. In yet other embodiments, the heat conductor includes a portion located on the crystal blank in the inner space.
In another aspect, the invention is directed towards a piezoelectric oscillator including the foregoing piezoelectric resonator unit, an oscillation circuit that is electrically connected to the piezoelectric resonator, a temperature sensor, a heating element, and a control circuit that controls the temperature sensor and the heating element.
According to the above-described configurations, a portion of the heat conductor is arranged in the inner space in which the piezoelectric resonator is hermetically sealed. As a result, the temperature of the piezoelectric resonator can be accurately detected and the piezoelectric resonator can be effectively radiated with heat. In other words, a piezoelectric resonator unit can be provided in which the piezoelectric resonator is effectively radiated with heat on the basis of accurate changes in temperature, and therefore temperature control can be appropriately performed on the piezoelectric resonator.
In yet another aspect of the invention, the invention is directed towards a method for controlling the temperature of the piezoelectric resonator unit described above. The method includes (a) detecting a temperature of the piezoelectric resonator via the heat conductor portion of the heat conductor using the temperature sensor, (b) determining an amount of heat to be supplied to the heat conductor portion of the heat sensor by the heating element on the basis of the temperature detected in (a), and (c) radiating heat onto the piezoelectric resonator via a portion of the heat conductor located in the inner space using the heating element on the basis of the amount of heat to be supplied determined in (b).
According to the above-described configuration and method, because a portion of the heat conductor is arranged in the inner space in which the piezoelectric resonator is hermetically sealed, the temperature of the piezoelectric resonator can be accurately detected and the piezoelectric resonator can be effectively radiated with heat. In other words, a temperature control method can be provided in which the piezoelectric resonator is effectively radiated with heat on the basis of accurate changes in temperature, and therefore temperature control can be appropriately performed on the piezoelectric resonator.
The present invention can provide a piezoelectric resonator unit and a temperature control method therefor, and a piezoelectric oscillator in which the temperature of a piezoelectric resonator can be accurately detected and temperature control can be appropriately performed on the piezoelectric resonator.